r igraph most connected nodes

Question

I have a graph:

paths = data.frame(from=c(10,20,30,10,30), to=c(20,30,50,30,60))
g <- graph_from_data_frame(paths, directed=FALSE)
plot(g)

Is there a command to find out the number of connections of each node, and find the most connected node. In this example 30 is the most connected node, with 4 connections. Then come 20 and 10 with 2 connections each.

Answer 1

In this case you can just calculate it from the data.frame, by counting number of connections (treating from & to as the same, since the appearance of a node in either vector means 1 connection):

sort(table(c(paths$from, paths$to)), decreasing = TRUE)

Result:

30 10 20 50 60 
 4  2  2  1  1 

Explanation: The code is creating a vector of all connections ( c(paths$from, paths$to) ), then counting frequency ( table ), then sort ing the result to get an ordered list, from most to least connected ( decreasing=TRUE ).

Answer 2

Here to find number of connections, you just need to count the appearance of each number in the data.frame , for example, 10 appears twice, the number of connection is 2. You can use rle , which returns an object with two attributes:

result <- rle(sort(c(paths[,1], paths[,2])))

> result
Run Length Encoding
lengths: int [1:5] 2 2 4 1 1
values : num [1:5] 10 20 30 50 60

And you can get its count by result$values , also you could make the result into a data.frame :

> data.frame(dot=result$lengths, count=result$values)
  dot count
1   2    10
2   2    20
3   4    30
4   1    50
5   1    60

Answer 3

Try this

lengths(as_adj_list(g))
# 10 20 30 50 60 
#  2  2  4  1  1 

Or try this using the colSums function from Matrix :

library(Matrix)
colSums(g[])
# 10 20 30 50 60 
#  2  2  4  1  1

which.max(colSums(g[]))
# 30 
#  3 

max(colSums(g[]))
# [1] 4